Well bottom treatment

ABSTRACT

Microcracks are formed in the environs of deep drilled wells, such as oil wells, by heating and then cooling the adjacent strata. This can be accomplished by introducing ammonia into the stratum water at the bottom of the well. The resulting heat of dissolution will slightly heat the strata adjacent to the bottom of the well as the ammonia will chemically assist the displacement of recoverable materials lodged in these strata. The cooling to the initial temperature of the bottom can be accomplished by the presence of additional stratum water in the well.

United States Patent 11 1 Ban et al. Dec. 4, 1973 [5 WELL BOTTOMTREATMENT 3,101,781 8 1963 Connally, Jr 166 273 3,123,136 3/1964 Sharp[75] Inventors. Akos Ban, Sandor blagy, both of 3,303,878 2/1967Connally Jr. Budapest} l Balm, 3,333,632 8/1967 Kyte Nagykamz ll o H ngry 3,384,177 5 1968 Day et al. 3,392,782 7/1968 Ferrell et al. [73]Assgnee' $3233 fi r g g Vanda, 3,464,492 9 1969 Friedman 166/274 xFiled; 1971 Primary Examiner-Stephen J. Novosad [21] Appl; No: 193 593AttorneyGabriel P. Katona [30] Foreign Application Priority Data [57]ABSTRACT Oct. 6 1970 Hungary KO 2368 Microcracks are formed in theenvirons of deep drilled wells, such as oil wells, by heating and then521 US. Cl. 166/302 166/308 the adjacent This can be acmmplished 51 Int.Cl E2lb 43/24 13216 43/26 by immducing ammmia into the Stratum water[58] Field o{Search 166/302 6 273475 bottom of the well. The resultingheat of dissolution 166/305 308 will slightly heat the strata adjacentto the bottom of the well as the ammonia will chemically assist the dis-[56], References Cited placement of recoverable materials lodged inthese strata. The cooling to the initial temperature of the 3 138 204 lh g f PATENTS bottom can be accomplished by the presence of addi- 'C arS011 166/305 R t l t t t th 1] 2,813,583 11/1957 Marx et al. 166/271Iona S ta um wa er m we 2,776,714 1/1957 Stanclift, Jr. et al 166/305 R3 Claims, N0 Drawings WELL BOTTOM TREATMENT In the environment of deepdrilled wells, particularly of hydrocarbon wells of various designations(prospecting, production, observation or medium injection) in additionto the finer fractions of the rock quite often resinous-bituminous andother materials are deposited which choke the pores in the stratumthereby impeding the seepage properties of the layer. As a result ofthese depositions the production, i.e. absorption capacity of the wellsdeteriorates.

When water and other media (e.g. gas) are injected into the hydrocarboncontaining strata, seepage is reduced and thereby the absorptioncapacity of the strata deteriorates also because of the surfaceproperties at boundaries between the different phases.

In order to improve the productivity, i.e. absorption capacity of wellsvarious methods have been applied to the treatment of the well bottomenvironment (layer blasting, acidification, treatment with organicsolvents, treatment with surfactants, etc.)

Of the hitherto known methods for stratum treatment the best resultswere obtained with layer blasting. Blasting of the stratum has, however,the drawback of forming substantially larger than intended, so-calledmacrocracks in the environment of the well bottom, said cracks beingcapable of penetrating into some undesirable parts of the stratum,moreover in some given case even into other strata. These cracks make itpossible for the stratum water and for the free gases to flow in anundesirable manner into the environment of the well bottom due to thefact that the cracks may extend into more distant regions in certaindirections, while in certain directions the permeability of the rock inthe environment of the well bottom is not improved.

Because of this phenomenon stratum blasting in the environment of thewell is rather problematical. In order to eliminate these drawbacksstratum blasting is often combined with the thermal or chemicaltreatment of the well bottom environment.

The present invention intends to help in the elimination of thesedrawbacks.

The present invention relates to a method which jointly contains theadvantages of the hitherto known methods and, at the same time,eliminates the known drawbacks of stratum blasting. In the course of ourexperiments we found that if the rock in the environment of the wellbottom is slightly heated and then cooled under the action of thetemperature of the stratum water to its initial temperature, a multitudeof microcracks will be formed in the stratum in all directions. At thesame time, as the result of such minor effects, no larger cracks(macro-cracks) are formed which could enable the penetration ofsubstances saturated in the stratum to some distant point, or ofsubstances saturated in other strata into the environment of the wellbottom.

As disclosed in our copending application, Ser. No. 193,429, filedsimultaneously herewith, we found in our further experiments thatammonia and its aqueous solution, due to their favourable adsorptionproperties towards the material of the rock matrix, are suitable for thedisplacement of the membrane of hydrocarbons saturated in the rock andbound polarly to the wall of the rocks as well as for the displacementof resinous and bituminous materials from the gaps in the rock, by beingadsorbed in place of said materials whereby entirely identical resultsto those achieved by the chemical treatment of well bottoms areobtained.

Ammonia is readily soluble in water even at high pressure to kg/cm) andat its critical temperature (132.4C). During its dissolutionconsiderable heat is liberated, the specific gravity of the solutions islower than the initial specific gravity of water (specific volumeincreases) and by applying different dissolution ratios, any solutionwith some arbitrarily chosen specific gravity adapted to the specificgravity of the substances saturated in the stratum can be prepared.

In carrying out the method in accordance with the invention, provided nowater is to be found in the stratum in the immediate vicinity of thewell bottom, first of all water is injected into the environment of thewell bottom. If there is some stratum water present in the environmentof the well bottom this stratum water is being used by introducingammonia thereinto.

As a result ammonia will dissolve in situ in the water in the immediatevicinity of the well bottom, and the liberated considerable amount ofheat of dissolution will exert the above described thermal effect and atthe same time the ammonia or its said solution will subject the stratumto chemical treatment.

With the help of the injected ammonia the specific gravity of thestratum water, or of the previously injected water into the environmentof the well bottom, can be brought to agree with the specific gravity ofhydrocarbons saturated in the stratum.

By means of the application of said method a layer of considerably moreextensive and more uniform permeability and with this a greater increasein productivity can be achieved when applied with or without stratumblasting to petroleum and gas production, as well as to water and othermedia injecting wells, than with any of the hitherto known methods oftreatment.

What we claim is:

1. In a process for increasing the permeability of strata in thevicinity of well bottoms without creating a substantial amount ofmacrocracks therein, wherein naturally occuning or externally introducedwater is present in said vicinity, the improvement which comprisesgenerating heat in situ in said vicinity by injecting ammonia into thewater present in said vicinity, whereby the heat of dissolution of theammonia results in the formation of microcracks.

2. The improvement in the process of claim 1, wherein gaseous ammonia isinjected into the water in the vicinity of the well bottom.

3. The improvement in the process of claim 2, wherein the amount of theinjected ammonia is such that the resulting aqueous solution thereofwill have a specific gravity approximating that of the hydrocarbons insaid strata under the given temperature and pressure conditions.

2. The improvement in the process of claim 1, wherein gaseous ammonia isinjected into the water in the vicinity of the well bottom.
 3. Theimprovement in the process of claim 2, wherein the amount of theinjected ammonia is such that the resulting aqueous solution thereofwill have a specific gravity approximating that of the hydrocarbons insaid strata under the given temperature and pressure conditions.